Common force field for graphite and polycyclic aromatic hydrocarbons

A valence force field based on Huckel's theory has been developed, which al lows us to establish a close correlation between phonons of graphite and th e normal modes of small polycyclic aromatic hydrocarbons (such as coronene and hexabenzocoronene). The results show that in these systems two kinds of motions dominate the Raman spectrum: the (sic) mode and the "breathing" a mode. These modes are the equivalent, in a finite domain, of the E-2g phono n of graphite at the Gamma point and the A' phonon at the K point of the fi rst Brillouin zone. This study provides a useful basis for the understandin g of the Raman spectra of any material containing sp(2) carbon domains. [S0 163-1829(99)01542-8].